My interpretation is that it was an open ending up to what we want to believe as viewers. I think in a way, one of the message here is that we always like to imagine how a star live their lives. You can say that knowing how Doona and Won Joon had that final scene hugging each other, we are still imagining what had happened to them afterward. Questions like, did they get back together or are they fully over now with no chance of crossing paths again?
We would discard the ending we do not like and choose to believe what we want. But one thing to note is the amount of sacrifice that goes into relationship especially for a celebrity that receive the public's love. Whether Doona did get back with Won Joon or not, both can be considered viable ending that is not truly bad. The last montage where we never see them being together after the hugging scene prove that they are still doing what they excel in. They share good memories with one another, and they missed each other dearly. With those, they became "better individuals" whom have their lives change forever because of each other. Won Joon being the guy that pulled Doona out of her slump and influence her to take control of what she wants to do in life. Doona whom brought joy and essentially allow Won Joon to express himself as a person with weakness instead of just being restraint.
Overall, I enjoyed the short drama a lot. Doona is a bae indeed XD.
